Parxer.—On Notornis mantelli. 249 
and 4a (pl. XXI.), the former showing the outline of the sternum of 
Notornis from the ventral face with that of Ocydromus superposed in dotted 
outline on the left side, and that of Porphyrio in broken outline on the 
right ; while fig. 44 shows the right half of the sternum of Notornis with 
that of Tribonyx superposed in dotted outline. 
The sternum of Notornis is broad and flat; its anterior edge is somewhat 
emarginate, as in Ocydromus, and is devoid of all trace of the manubrium or 
rostrum (fig. 4, 4a, r) found in Porphyrio, and toa less degree in Tribonyx. The 
coracoid grooves are even more widely separated than in Ocydromus, instead 
of having merely the width of the rostrum between them, as in the other 
genera. The diminution in width of the sternum from its anterior to its 
posterior end is very gradual; in this respect Notornis ag —_— aneneeies 
Tribonyx. The external xiphoid processes (e. x.p.) are divergen 
at their distal ends, and are ceugeitiniale shorter she in either of the 
allied genera; the middle xiphoid process is blunt and unossified, the bone 
terminating in a straight transverse edge, about six mm. from the actual 
extremity of the process. In this again the resemblance between Notornis 
and Tribonyz is of the closest kind: the middle xiphoid both in Porphyrio 
and Ocydromus is completely ossified, terminating in the former by a trun- 
_ ated edge, while it is deeply emarginate in the latter. 
The keel of the sternum is feebly developed, being hardly deeper, pro- 
_ portionally to length of trunk, than that of Ocydromus. Its anterior edge 
4 has nothing of the strong forward convexity found in Porphyrio, but passes 
almost insensibly into the ventral edge ; in this respect the resemblance to 
_ Ocydromus would be great, but for the fact that in the latter a strong bifid 
_ thickening (fig. 4, k) is formed at the junction of the anterior and ventral 
borders, whereas the corresponding thickening in Notornis is less marked 
and shows no tendency to division ; the resemblance to Tribonyr is here 
_ very marked. 
Another point connected with the flightlessness of Notornis is the very 
slight lateral curvature of the sternum; its two sides enclose a dihedral 
angle (fig. 5 8.) which is nearly as open as that of Ocydromus (a) and con- 
Siderably greater than in Tribonyx or Porphyrio(c and p). This transverse 
sternal angle as it may be called, seems to be pretty constantly more open in 
flightless birds than in the normal members of the same group; its increase, 
and the correlated diminution of the keel, cause the sternum to ee 
to the ratite type, as is especially well seen in Didus, Cnemiornis, 
* 
and Aptornis, and to a less extent in Nesonetta, Ophea se 
On the whole the sternum of Notornis differs from that o 
3 much the : aaiiie WAY. as the latter from that of Pe rphyri 
